1. Field of Invention
This disclosure relates to earth boring rotating cone bits, and particularly to providing a seal having a self break-in property on sliding engagement surfaces of the cone and the mating bearing pin.
2. Description of Prior Art
Drill bits used in drilling of subterranean well bores typically comprise drag bits and roller cone bits. Roller cone bits typically comprise a body having legs extending downward and a head bearing extending from the leg towards the axis of the bit body. Frusto-conically shaped roller cones are rotatably mounted on each of these journals and are included with cutting teeth on the outer surface of these cones. As the bit rotates, the cones rotate to cause the cutting elements to disintegrate the earth formation. Because of the high stresses incurred during drilling operations, the bearing mating surfaces within the bit require a bearing material or a surface treatment to sustain the loads and extend the bit life.
The cylindrical portion of bearing pin and cylindrical cavity of the cone define a journal bearing. Thrust bearing surfaces are located between flat portions of the bearing pin and cone cavity. The bearing spaces between the cone and bearing pin are filled with a lubricant. A pressure compensator equalizes pressure of the lubricant with the hydrostatic pressure on the exterior. Roller cone bits typically include a seal or a seal assembly to seal lubricant within the bearing and keep debris out of the bearing.
During operation of the drill bit the seal assembly experiences sliding contact with the leg or one of its components. Alternatively, some sliding contact may be experienced with respect to the cone. Sliding contact may present a problem when as machined roughness or other effects of machining, are present on a sliding surface. During the early life of the components, the protrusions of the as machined roughness may damage corresponding sliding surfaces before they are worn down by the sliding action. The damage caused by as machined roughness is especially prevalent when the corresponding sliding seal surface comprises a non-metal material such as an elastomer. In some alternative embodiments, the entire seal assembly comprises one or more seals comprised of an elastomeric material. Accordingly a need exists for eliminating potential damage caused by as machined roughness onto elastomeric seals.